Directional radio receiver



Aug. 2, 1949.

G. S. BURROUGHS Filed Jan. 8, 1946 DIRECTIONAL RADIO RECEIVER 2Sheets-Sheet 1 a: 5 Raga 1? DEMODUL 470/? I g E? HEATERS ATTORNEY Aug.2, 1949.

G. S. BURROUGHS DIRECTIONAL RADIO RECEIVER Filed Jan. 8, 1946 2Sheets-Sheet 2 /1? F/PoM MODl/ZATOI? [Pica/V5,? l 18 C i- DEMOOZ/MW/FF/POM MODUL/IT/IVG SOURCE I 1- Patented Aug. 2, 1949 UNITED SDIRECTIONAL RADIO RECEIVER Application January 8, 1946, Serial No.639,845

Claims.

My invention relates to directional radio receivers, particularly toreceivers for visually indicating the direction of received radio waves.

Directional radio receivers, such as so-called homing devices and radiocompasses, usually have moving mechanical parts including motors,commutators, and revolving loop antennas. In addi tion to the mechanicaldisadvantages of such equipment, the electrical circuits arecomplicated, are not easily adjusted and do not produce an easilyinterpreted signal.

An object of my invention is a simplified directional radio receiver.

A further object of my invention is a directional radio receiver that ismechanically and electrically simple, and which produces an easily interpreted visual indication of direction.

My invention is defined in the appended claims and preferred embodimentsare described in the following specification and shown'in theaccompanying drawing in which:

Fig. 1 is a diagrammatic showing of the circuits of one direction finderembodying my invention,

Fig. 2 shows the wave form of current in various parts of the circuitsof Fig. l, and

Fig. 3 is a diagrammatic showing of another embodiment of my noveldirection finder.

The essential elements of my novel receiver are the loop I, or otherdirectional antenna having in combination with antenna 1, a cardioidfield pattern, the cathode ray tube 2, the balanced modulating stage 3,the receiver 6 comprising the usual radio frequency amplifier anddetector or demodulator, and the alternating current source 5. The

loop may be fixedly mounted on the craft to be guided or may be manuallyrotated. The cathode ray screen shows a single radial line extendingradially from near the center of the screen to its edge, much like thepointer of a meter. As the loop rotates, the line turns about the screencenter, the angular position showing whether the transmitter, to whichthe receiver is tuned, is ahead or is to the right or left. The pointermoves from one side of center to the other as the loop rotates throughthe true bearing position.

Specifically, the terminals of the loop I, balanced and grounded at itselectrical center, are coupled in push-pull to the grid input circuitsof the balanced modulator 3. The modulator is two side-by-side amplifiertubes such as triodes enclosed in a common or in separate envelopes, asdesired. The anode or output circuits are connected in parallel to theinput of the receiver and demodulator 4. Alternating current from thesource 5 is applied in push-pull to the triode control grids. The sourcemay be a commercial power transformer having a secondary winding 6 witha grounded center tap, and designed for and connected to a power sourceof commercial cycle energy. or to the 400 cycle alternating cur-- rentsupply of an aeroplane.

A sense antenna 1 is coupled through appropriate phase shifting means tothe output of the modulator.

In operation, with the loop turned to one side a small angle from itsnull position, the low frequency modulating wave A from A. C. source 5,Fig. 2, combines with the radio frequency wave of the loop to producewave B at the output. The sense antenna output C added to B results inWave D at the input to the receiver 4. The audio output of the receiveris then wave E, corresponding in frequency to the modulating wave fromtransformer 5. If, now, the loop is turned to a position on the otherside of the null, the phase of the radio frequency voltage in themodulated wave B will be reversed degrees so that when wave B iscombined with the sense wave C, there is obtained wave F at the receiverinput and wave G at the output. That is, when the loop is turned to theleft, say, of the null, the receiver output is the same frequency andphase as the modulating voltage, and when the loop is turned to theright of the null, the receiver output is 180 degrees out of phase withthe modulating voltage. The amplitude of the receiver output varies inproportion to the amount the loop is turned away from the null. With theloop directly on the null. the demodulator output is zero. Hence, bycomparin the phase of the demodulator output with the modulatingvoltage, the right-left bearing position of the loop may be indicated.One con venient means for making the comparison is a conventionalcathode ray tube with magnetic or electrostatic deflection. Zero centervoltmeters of various electrodynamometer or electrostatic types could beused for the same purpose. The cathode ray tube shown comprises theusual control and accelerating electrodes 8, 9 and I0, and beamdeflecting coils II and 12 for moving the beam in two orthogonaldirections over the fluorescent screen If of the tube. One deflectioncoil, say the coil for horizontal deflection of the beam, is connectedto the output of the demodulator, while the vertical deflection coil isconnected to the modulating source, a separate secondary winding M onthe transformer being used if desired.

When raw alternating current is applied to the voltage divider l5 forsupplying the cathode ray tube electrodes, the cyclic variations inpotential affect all the electrodes in phase and thus do not disturb theproper voltage ratios for focusing the beam on the center of the screen.The spot however is extinguished during the negative half cycle and isilluminated during nearly all of the positive half cycle. With the A. C.voltage applied to the. vertical deflection coil the beam tends to movevertically. The deflection sensitivity of the beam is being cyclicallyvaried because of the cyclically varying potentials applied in theaccelerating electrodes. The A. C. voltages applied in the deflectioncoils also vary cyclically in synchronism (being derived from the samesource 5), with said potentials and tend to oppose them in their efiecton the beam. However, the deflection of a magnetically deflected cathoderay tube is inversely proportional to the square root of theaccelerating voltage and directly proportional to the deflectingvoltage. Hence the forces do not balance and a'radial line is tracedduring the positive half cycle.

By applying another alternating current voltage to the horizontaldeflection coil in phase with the vertical deflection field, the line oflight will incline to one side of the initial vertical posttion, and ifthe voltage applied, to the horizontal coil-is 180 degrees out of phasewith the vertical deflection field, the line will incline to the otherside the extent'of inclination being determined by the amplitude. It isapparent now that if the" output of the demodulator is applied to. thehorizontal coil and the modulating voltage is applied to the verticalcoil the inclination of the line of light will instantaneously andaccurately indicate the right-left direction of the loop antenna withrespect to the direction of the received radio wave.

A clear, sharp line, on the screen for accurate direction indication.may be insured by a filter it connected in the output of the demodulatorand designed to reject all frequencies except the single frequency ofthe modulating source. Herein lies an importantfeature of my invention.Since there are no commutators or slip rings with brushes, and no sourceof local electrical disturbances or spurious oscillations, it is onlynecessary for filter 6 to protect the deflection fields from receivedcarrier modulations, noise, and the like. The efiective filter may, inmost systems of myinventiomcomprise simply a series resistor l1 andshunt condenser 13, as shown in Fig. 3..

The sensitivity of the cathode ray tube to changes in loop position maybe materially increased by adjustingv the audio, output Voltage appliedto the vertical deflection coil to a value greater than the. voltageapplied to the horizontal deflection coil.

The voltages, to be compared can with equal facility be applied, to. thedeflection plates of a conventional electrostatic cathode ray tube, assuggested in Fig. 3 in they following manner. lhe control andaccelerating electrodes 3, 9 and it, should be energized with directcurrent, and may be, tapped to the potentiometer it which is con nectedacross a high voltage D. C. power supply {9. One pair of deflectionplates 28 and 2! are connected. across the output circuit of thedemodulator, and, the other pair of deflection plates ZZ'and. 23 are,connected across the alternating modulating source. The deflectingvoltages for the two pairs of plates are developed, respectively, acrossthe high, ohmic resistors 2t and which are. each connected at onev end.to the positive side of the high voltage potentiometer is so that thealternating deflection voltage moves the beam equal distances eitherside of center. The voltages are preferably adjusted to extend the lineof light from edge-to-edge of the screen. [is before the line pivotsabout the screen center in response to rotation of the loop antennaeither side of null.

lvly improved directional radio receiver is mechanically andelectrically simple, is easy to adjust, and produces an easilyinterpreted visual indication of direction.

I claim:

1. A radio direction finder comprising, a directional antenna; a cathoderay tube having a fluorescent, screen, a cooperating electron beamsource, control electrodes for said electron beam and magnetic electronbeam deflection elements; an alternating current source, means formodulating'the radio frequency waves appearing at the terminals of saidantenna with the waves of difierent phase from said source, ademodulator connected to the modulating means for deriving the modulatedwave, connections between the electron beam deflection elements,respectively,

, and the output of said. demodulator and said alternating currentsource and. means for energizing saidv control electrodes with, wavesfrom said alternating current source.

2. In aradio direction finder, a, modulator, said modulator comprising:two. electron discharge devices each having a cathode, a control grid,and an anode; a directional. receiving antenna balanced with respect toground, so. that the phases of the radio frequency voltages appearing atthe terminals. of the antenna are opposed, couplings between said.terminals, respectively; and. said control grids, a souroeoi modulatingvoltage connested in push-pull to said grids, a non-directional antenna,a demodulator, theinput of said demodulator being connected to, saidnon-directional antenna and to said anodes, a cathode tube. comprisingan electron beam source, control electrodes for said electron beam, two0;- thogonal magnetic beam deflecting means, said deflecting means,being connected, respectively, to the output of said. demodulator andtosaid source of modulating voltage and means for energizing saidcontrol electrodes with waves from said, alternatingcurrent source.

3. A direction finder comprising an antenna loop, the electrical centerof the loop being grounded, two amplifiers, an alternating voltagesource, a transformer winding with a grounded center tap, means forenergizing said winding with energy from said alternating voltage sourceone terminal of said loop and one terminal or" said winding beingcoupled together and connected to the input circuit of one of saidamplifiers, the remaining terminals of said loop and said transformerbeing coupled together and to the input circuit of the other amplifier,a sense antenna, a demodulator, the output circuits of said amplifiersand, said; sense antenna being connected together and to the inputcircuit of said demodulator, and, a cathode ray oscillograph forcomparing the, phase of the output of said domodulator with the phase ofthe voltage across said transformer winding comprising an electron beamsource, control electrodes for electron beam, two sets of magneticdeflection elements means for applying the output of said demodu latorto one set of deflection elements, means for applying energy from saidalternating voltage source to another set of deflection elements andmeans for applying energy from said alternating voltage source to saidcontrol electrodes.

4. A direction finder according to claim 3 comprising a filter forselectively passing the modulations of said modulator, connected betweensaid demodulator and said cathode ray oscillograph.

5. A right-left radio direction finding system comprising a directiveantenna system, a source of alternating voltage, means for modulatingthe output of said directive antenna system in pushpull with saidalternating voltage to produce an effective angular sweeping of thedirective pattern of said directive antenna system, means fordemodulating the output of said antenna system, a cathode rayoscillograph comprising an electron beam source, control electrodes forsaid electron beam, and sets of magnetic deflection elements, means forapplying said demodulated antenna system output to one set of deflectionelements, means for applying said alternating voltage to another set ofdeflection elements and means for applying said alternating voltage tosaid control electrodes.

6. An arrangement according to claim 5, further comprising anomni-directional antenna and means for combining the output of saidomnidirectional antenna with said modulated antenna output beforedemodulation.

GORDON S. BURROUGHS.

REFERENCES CITED The following referenlces are of record in the file ofthis patent:

UNITED STATES PATENTS

